Processes of separating nitrile-hydrocarbon mixtures by means of phenols



Patented 31, 1939 I UNITED STATES PATENT OFFICE PROCESSES OF SEPARATINt}NlTRlLE-HY- DROCABBON MIXTURES BY MEANS OF PHENOLS Anderson w. mum andWilliam 0. Pool, cm-

oago, 111.,

assignors to Amour and Company,

Chicago, 111., a corporation of Illinois No Drawing. Originalapplication July 9, 1938, Serial No. 89,850. Divided and thisapplication October 15, 1937, Serial No. 169,328

8 Claims.

This invention relates to processes of separatlng aliphatic nitrilesfrom admixtures thereof with hydrocarbons and it comprises processeswherein such mixtures are treated with a preferentlal solvent materialfor the nitriles to form an extract phase containing the nitriledissolved in the solvent and a hydrocarbon phase, the two phasesseparated and the nitrile then separated from the extract phase. I

Recently processes have been described, as in U. S. Patents 1,991,935,2,033,536 and 2,033,537, for preparing nitriles of relatively lowmolecular weight fromnitriles of high molecular weight. For example, bymethods of pyrolysis higher aliphatic nitriles such as stearo andpalmitonitrile can be "cracked to give reaction products con tainingnitrileshavlng four, five, six and seven carbon atoms. The crackingoperation can be so controlled that nitriles of almost any desirednumber of carbon atoms say from six to eleven can be prepared fromnitriles of higher molecular weight. In these processes the reactionproducts are homogeneous liquid mixtures containing various nitrilesassociated with quantities of aliphatic hydrocarbons.

'Although the cracked reaction mixtures have many uses as such withoutfurther treatment, there are many instances whenit is desirable toseparate the nitriles from the hydrocarbons and to then fractionallydistil the separated nitriles. And the pure nitriles are startingmaterials for many organic synthesis since they are sources of polaraliphatic compounds having from six to about eleven carbon atoms-Hitherto reactive compounds of this nature have not been available on acommercial scale and at a price which would enable them to be used'ingreat quantities. In other words, the development of processes ofpreparingnitriles from the cheap fatty acid sources has made it possible.or us to'supply large quantitles of aliphatic compounds having fromabout five to ten carbon atoms in the alkyl group, together with ahighly reactive polar, or CN group. This means that many aliphaticamines, alcohols and acids, of from six to. ten carbon atoms can beprepared at low cost. Hitherto these materials have been so expensivethat they could not I be used in the arts.

As stated, mixtures of nitriles alone can be separated readily byfractional distillation. It is difiicult, however, to separate mixturesof the nitriles and hydrocarbons in this manner. Constant boilingmixtures areobtained in many instances and there are other objections.The.

, treated with preferential solvents in such a manner that the nitrilesare dissolved to the exclusion of the hydrocarbons. From the extractphase of nitriles and solvent we can then recover the nitriles andrecover the solvent for reuse. Many experiments have been necessary,however, since what will or will not act as a preferential solvent forsuch mixtures could not be determined in advance of experiment. Manysolvents which might seemingly dissolve the nitriles without affectingthe hydrocarbons actually form homogeneous mixtures without leading tothe formation of stratified layers of hydrocarbon and nitrile extract.Because of the pronounced mutual solubility of the nitriles and ali-This leads to mutual solution of all constituents. I Consequently, thesearch for satisfactory preferential solvents has been a difllcult taskand many unexpected discoveries have been made.

For example, we have discovered that watery solutions of aliphaticalcohols can be used successfully provided care is taken to control thequantity of water present. Thus a percent solution of methyl alcoholwill dissolve the nitrile but not the aliphatic hydrocarbons present butpercent methyl alcohol forms a homogeneous solution of alcohol, water,nitriles, and hydrocarbons. Hence the application of the broad, old,idea of preferential extraction with a suitable solvent to mixtures ofthe type with which we are concerned has not been a simple matter.

Moreover, having discovered a suitable preferential solvent which willgive an extract containing nitriles dissolved in the solvent, the 'nextstep is the liberation of the dissolved nitrile from the nitriletherefrom; What we have sought is solvents which would dissolve thenitriles but not the hydrocarbons, which would givegood cleanstratification into two liquid layers, and which, by the additionof'something to the extract layer, would then liberate the nitrile.These requirements have made the search for solvents prolonged.

We have, however, discovered four classes of compounds which can be usedin our process and, since we are the first to deal with this problem,and to describe its solution, we claim our invention broadly in theappended claims. We believe ourselves'to be the first to propose the useof preferential solvents in this art in such a manner that the nitrilesare liberated from the extract phase by the addition of substancesthereto which decrease thesolubility of the preferential solvent for thenitrile in the extract.

We have discovered that aliphatic alcohols, phenolic compounds likephenol and the cresols, amino compounds generally aliphatic butincluding aniline, and the water soluble aliphatic carboxylic acids canbe used under certain conditions as preferential solvents and that fromthe extract phase composed of solvent and nitriles we can separate thenitriles simply by adding something to the extract which acts todecrease the solubility of the nitriles.

We shall first describeour invention with reference to the use of thealiphatic alcohols. All of the alcohols which we use are miscible withwater and among them we can use methyl, ethyl, propyl, both normal andiso, butyl, benzyl, furfuryl, tertiary butyl, secondary butyl, allyl,diamyl, secondary amyl and cyclohexyl. When using the alcohols we firsttreat the mixture of nitriles and hydrocarbons with a watery solution ofthe alcohol, the amount of water present being such that the nitrilesare soluble in the watery alcohol but the hydrocarbons are not. We thenseparate oif the upper layer of hydrocarbons from the lower extractphase composed of nitriles dissolved in the watery alcohol. Upon theaddition of more water to the extract so as to decrease the actualconcentration of alcohol the nitriles separate out since they are notsoluble in extremely diluted alcohol.

As stated the various alcohols listed above can be used but for the sakeof brevity we shall describe detailed examples using methyl alcohol.

One hundred parts by volume of a nitrile-hydrocarbon mixture obtained bycracking stearonitrile is mixed with 100 parts by volume of 75 percentmethyl alcohol (75 percent alcohol, 25 percent water). Stratificationoccurs and the upper layer' of hydrocarbons is separated off. Thesehydrocarbons still contain some nitriles and are advantageouslyre-extracted with 100 parts of percent methyl alcohol. The hydrocarbonlayer is again separated and again extracted with 100 parts by volume ofpercent alcohol. The final hydrocarbon layer, amounting to 60 volumes,contains only 0.1 percent nitrogen.

The three alcoholic lower layers, or extract phase, from the threeextractions are united and water added thereto until the nitrilestherein separate as an upper layer which can be readily decanted. Thisupper layer amounts to 40 parts and has a nitrogen content of 8.9percent. The methyl alcohol layer, after dilution as described, has aconcentration of about 60 percent methyl alcohol. It can be recoveredfor reuse by distillation.

Instead of using three extractions with increasing strengths of alcoholswe can extract directly with 80 percent methyl alcohol and get goodresults. Or the 80 percent methyl alcohol can be run into the top of acolumn of the nitrilehydrocarbon mixture and the extract phase recoveredcontinuously from the bottom of the column.

However, the strength of alcohol must be closely regulated so that it isstrong enough to dissolve nitriles but not hydrocarbons.

We find it desirable to start with fairly dilute alcohol, such as 75percent strength and then reextract the separated hydrocarbon layer withalcohol of increasing strength. The more dilute alcohol removes the verylow molecular weight nitriles which tend to make the hydrocarbonsmiscible with stronger alcohol. After the lower nitriles have beenremoved then the strength of the alcohol can be increased to 85 percentas described. If 85 percent alcohol were used directly a homogeneousmixture showing no Stratification of hydrocarbons would result.

Normal propyhalcohol can be used in the same manner and the sameconcentrations as methyl alcohol. When using the other alcoholsdescribed above preliminary experiments should be run to determine theappropriate strength of alcohol for the extraction. This can be readilydone on a small scale before treating large volumes ofnitrile-hydrocarbon mixture.

.We shall now describe modifications of our invention using aliphaticcarboxylic acids as preferential solvents. All the acids we use aremiscible at least to some extent with water. Among them can be mentionedthe following: acetic, propionic, acrylic, iso-valeric, normal valeric,isobutyric, normal butyric and caproic.

This modification is well illustrated by reference to the use of acetic.For example, we mix parts of nitrile-hydrocarbon mixture with 100 partsof glacial acetic acid containing 4 parts of water. The mixture iscooled to 0 C. at which temperature stratification occurs. The upperlayer or phase is composed of 56 parts of hydrocarbons containing 1.3percent nitrogen. The lower layer or extract phase amounting to 144parts contains the acetic acid and nitrile. To this lower layer we add100 parts of water which results in the :separation of an upper layeramounting to 52 parts which consists essentially of nitriles andcontains 5.5 percent nitrogen. Any acetic acid present can be removedfrom the nitrile layer by washing with water. The hydrocarbon layer canagain be extracted with the strong acetic acid to recover morenitrile'therefrom. All quantities above are parts by volume.

As stated above, phenols are also suitable solvents. Among them we canuse ordinary phenol, and ortho, meta, and para cresols. For example, wemix 100 parts by volume of the cracked nitrile mixture with 100 parts byvolume of phenol and 30 parts by volume of water. The mixture is cooledto 0? C. which gives three layers. The bottom layer consists essentiallyof pure water, the top layer contains 36 parts of hydrocarbons in whichthe nitrogen content is 0.6 percent. The middle layer amounts to 168parts by volume and contains phenol, water, and nitriles. To this middlelayer we add dilute sodium hydroxide solution, about a 10 percentsolution, until the nitrile is liberated. This gives us 64 parts byvolume of nitriles containing 6 percent nitrogen. If desired thehydrocarbon layer can again be extracted with more phenol solution.

Many different amines can also be used as preferential solvents. Amongthem may be mentioned aniline, ethyl amine, isopropyl amine, normalpropyl amine, diethyl amine, allyl amine,

benzyl amine, secondary butyl amine. isobutyi amine, normal butyl amine,isoallyl amine, normal amyl amine, dinormal propyl amine, pyridine,

diallyl amine and cyclohexyl amine. For example 100 parts by volume ofthe nitrile-hydrocarbon mixture is mixed with 100 parts by volume ofaniline and the mixture cooled to C. This gives an upper layerconsisting of 40 parts of hydrocarbons containing 0.5 percent nitrogenand a lower layer composed of 160 parts by volume containing aniline andnitriles. To this lower layer we add dilute hydrochloric acid solutionuntil the nitriles separate out. This givesv us 60 parts of a nitrilefraction containing percent of nitrogen. The aniline can be recoveredfor reuse by treating the solution of aniline hydrochloride with dilutecaustic soda. 7

In the appended claims we denote the layer of nitriles dissolved in thepreferential solvent as the extract phase.

This application is a division of our co-pending application Serial No.89,850 flied July 9, 1936 wherein we specifically claim the use ofaliphatic alcohol solutions as preferential solvents.

Having thus described our invention, what we claim is:

l. The process of separating aliphatic nitriles from admixture thereofwith hydrocarbons which comprises treating the mixture with apreferential solvent composed of an aqueous phenolic solution containingat least about 70% of a phenol to give an extract phase containing thenitriles dissolved in said preferential solvent and a hydrocarbon phase.separating the phases, adding enough dilute alkaline solution to theextract phase to liberate the nitriles therein as a layer, andseparating the nitrile layer.

2. The process of separating aliphatic nitriles from admixtures thereofwith hydrocarbons, said mixture resulting from the cracking of highmolecular weight fatty acid nitriles, which comprises treating themixture with a preferential solvent composed of an aqueous phenolicsolution containing at least about 70% of a phenol to give an extractphase containing the nitriles dissolved in said preferential solvent anda hydrocarbon phase, separating the phases, adding enough dilutealkaline solution to the extract phase to liberate the nitriles thereinas a layer, and separating the nitrile layer.

3. The process as in claim 1 wherein the alkaline solution is a sodiumhydroxide solution.

4. The process as in claim 2 wherein the alkaline solution is a sodiumhydroxide solution.

5. The process as in claim 1 wherein the phenol is ordinary phenol.

6. The process as in claim 2 wherein the phenol is ordinary phenol.

"l. The process as in claim 1 wherein the mixture of nitriles,hydrocarbons and a mixture of water and phenol is cooled to atemperature of about 0 C.

8. The process as in claim 2 wherein the mixture of nitriles,hydrocarbons and a mixture of water and phenol is cooled to atemperature of about 0 C.

ANDERSON W. RAIBTON. WIILIAM O. POOL.

